Satellite DNA's and other simple, tandemly repeated nucleotide sequences are present in or about the centromeric heterochromatic regions of the chromosomes of man and numerous other eukaryotes. Their functions are unknown. We seek support to continue our studies of satellite DNA's in Drosophila. We will employ established biochemical, genetic, and cytological procedures to extend our investigation of satellite DNA's and chromosomal proteins. The proposed experiments may provide information about: 1) The arrangement of satellite DNA sequences along the chromosome; 2) The possibility that Drosophila satellites are compacted into centromeric heterochromatin by phosphorylated H1 histones; 3) The effect of H1 phosphorylation on the in vitro preference of H1 histones for satellite DNA's in D. virilis; 4) The possible effects of phosphorylation on the conformation of Drosophila H1 histones; 5) The amino acid sequence of the phosphorylated pentadecyl peptide in Drosophila H1; 6) The location of the phosphorylation site in the H1 molecule; 7) Factors controlling the phosphorylation of Drosophila H1. Since satellite DNA's and H1 histones are chromosomal features common to Drosophila and to man, there is an excellent possibility that these experiments will provide information applicable to the problem of organization and molecular architecture of human chromosomes.